Tape printers are well-known for unwinding and running wound long tape by a direct current motor (designated as DC motor hereinafter) and performing line printing on the unwound tape by using dot patterns. Some of such tape printers are provided with a cutter for cutting the tape downstream from the printing position. A printed strip having a desired length is produced because the original tape can be cut manually or automatically after printing.
The above tape printers may be provided with an encoder to detect an amount of rotation of the DC motor. The encoder has a rotary disk having radial slits formed peripherally at regular intervals. The disk is connected to an output shaft of the DC motor. The encoder has a photo-sensor having a light-emitting element and a light-receiving element disposed at the opposite sides of the rotary disk. When the encoder is used, the printing head is driven to print on the tape, every time the amount of rotation of the DC motor increases by a predetermined amount based on an output pulse signal of the light-receiving element. This arrangement allows the tape to be constantly printed at uniform dot intervals in the running direction of the tape, regardless if the tape runs at a constant speed or not.
As described above, when the timing of driving the printing head is always determined according to the output signal of the encoder, the printing cycle may become short when a change in the rotations of the DC motor is large and the DC motor rotates at a high speed. Therefore, unless high performance hardware is provided, it is difficult to secure a time period sufficient for a printing data processing which is performed while the printing head is at rest such as development of outline font data into bit map data, character ornamentation, and conversion of vertical lines into horizontal lines and vice versa. Accordingly, deterioration of the quality of printed image such as Printing error may caused.
Therefore, it is a main object of the present invention to provide a tape printer that can secure a time period sufficient for processing printing data and print a high quality image if the DC motor rotates at a high speed in the case an encoder is used.